Interfacial Compounds Characteristic and Its Reliability Effects on SAC305 Microjoints in Flip Chip Assemblies

This study mainly focuses on site effects of the Ni pad interface on intermetallic compounds (IMCs) characteristic during assembly reflowing, and attempts to provide a reasonable explanation for this particular finding. Besides, the changes of the resulting IMCs characteristic are characterized during thermal shock (TS) cycling, and their potential influences on thermal–mechanical reliability of microjoints are evaluated experimentally and numerically. The results show that the site on the Ni pad interface of silicon chip has great influence on interfacial reaction products, i.e., interfacial IMCs. After bumps soldering, a great amount of larger diamond-shaped (Cu, Ni)₆Sn₅ compounds were densely packed at the edge region, while some smaller ones were only scattered at the center region. Moreover, substantial particle-shaped (Ni, Cu)₃Sn₄ compounds as well as some rod-shaped ones emerged at the spaces between the (Cu, Ni)₆Sn₅ compounds of the center region. More importantly, such site effects were remained in the microjoints during TS cycling, which induced the formation of larger protruding (Cu, Ni)₆Sn₅ compounds. Finite element (FE) simulation results showed that the stress was mainly concentrated at the top of the protruding (Cu, Ni)₆Sn₅ compounds, which can be a critical reason to cause the crack occurrence. Furthermore, the underlying mechanism of the interfacial IMCs characteristic induced by the site effects was attempted to propose during bumps soldering.